Last year, Nick Thompson, Professor of Psychology and Ethology of Clark University, dropped by Santa Fe on Sabbatical. Nick brought with him a puzzle relating to the Prisoner’s Dilemma.
The core idea of the Prisoner’s Dilemma is a game where two folks choose to cooperate or not (defect). The scoring is such that if you cooperate and your opponent defects, you (the “sucker”) get quite a low score. If you both cooperate, however, you get a reasonable score but not as high as a defector gets against a cooperator. This classic in game theory poses the paradox that your best move is to defect, even though if you both defect, you both get a very poor score. Grim.
Robert Axelrod was puzzled by this, and suggested that if the game were repeated (iterated), the best outcome would could vary according to the strategy of the players. This resulted in his now famous computer tournament pairing strategies against one another. The sweet result was that a firm but friendly strategy, Tit for Tat, which cooperated initially, then simply repeated the opponent’s previous move from then on, was the overall winner.
Nick, looking at this, thought that it’d be nuts to stay in a series of Prisoner’s Dilemma games if the opponent was clearly no fun to work with. Thus he introduced the idea of leaving the tournament. MOTH, My way Or The Highway, builds a new suite of strategies which have the additional capability of leaving an unpleasant encounter. This creates a pool of strategies without partners, so they are re-paired randomly, and the tournament continues.
The result is that Nick, along with several of our local Friam group here in Santa Fe, worked on a NetLogo model exploring this new approach. This model expanded upon and validated earlier work done by Nick and his colleagues David Joyce and John Kennison. This resulted in a paper delivered to the Lake Arrowhead Conference on Human Complex Systems.
The NetLogo Model we created is viewable by you, gentle reader. The explanation provided with the model presents considerable detail about the ideas behind the Moth strategy.
Not surprisingly, a quite successful strategy is a variation of Tit for Tat: play Tit for Tat and on the first defection by your opponent, leave the tournament to be paired with a (hopefully!) more cooperative player!
